C. H. Danforth

Nitrogen mustard as a teratogenic agent in the mouse.

Summary A single intra-abdominal injection of nitrogen mustard in an amount equivalent to about 1 μg per g of body weight and administered on the 10th to 12th day of gestation has no apparent effect on a pregnant mouse, but may have a pronounced effect on the young in utero. Some of the latter are killed outright and others show a wide range of resultant anomalies. Only anomalies involving the feet are reported here. The grades and distribution of deficiencies in the feet reveal a significant difference in responses on the 2 sides of the body and a considerable developmental autonomy on the part of each individual foot.

Cause of Hen-Feathering in Campine and Bantam Males.

In ordinary breeds of the fowl differences in secondary sexual characteristics of the plumage have been shown 1 to be due to endocrine factors which are largely controllable under experimental conditions. With the type of feather produced serving as a measure of response, evidence from various sources is consistent in indicating that in most breeds the follicles of the male and those of the female react in exactly the same manner to any set of stimuli. 2 In other words, sexual differences in plumage are referable to differences in endocrine stimuli rather than to differences in tissue response. Since this situation obtains in ordinary breeds of fowl, it has been natural to look for an endocrine causation of hen-feathering in those strains where the male has a plumage similar to that of the female. The prompt assumption of male plumage by the castrated Sebright, 3 which is normally hen-feathered, seemed at first to supply definite evidence of an endocrine causation for hen-feathering in the male. But cross-transplantation of testes in Sebright and Leghorn fowls 4 showed that the testes of hen-feathered Sebrights produce no special hormone different from that of cock-feathered Leghorns; and the experiments to be reported at this time indicate that follicles from a hen-feathered strain and those from a cock-feathered strain may produce their respective types of feathers when grown side by side and subjected to the same endocrine environment.

Hereditary doubling suggesting anomalous chromatin distribution in the mouse.

Mice with six legs appeared about two years ago in a stock which had descended from five individuals and had been inbred for several generations. Since this stock had been subjected to no special treatment, the possibility of the anomaly having a purely hereditary basis suggested itself, and in the fall experiments were undertaken to determine if such were the case. In the course of the tests many anomalous individuals have been produced ranging from Y-shaped specimens with four hind legs and two tails, to those with a relatively slight degree of doubling in the external genitalia. These may all be referred to as “doubles.” Apparently connected with the same manifestation is the appearance of hemorrhagic testes, spina bifida, and occasional other anomalies such as microphthalmia. The anomalous individuals are for the most part incapacitated for breeding, so their parents and sibs have been isolated from the rest of the stock and used for the experiments. At first anomalous individuals were produced about equally by the selected (D) and unrelated (B) strains, but gradually the former began to show an increased incidence which has risen to about 12 per cent (113 :805) for the whole A strain and about 20 per cent (45:178) for the best producers. In the meantime doubling has been practically eliminated from the B strain, only two anomalous individuals having appeared among the last 1100 or more young. In a few instances the character of the anomaly has been such as to permit of the production of young, and one mating between two anomalous individuals has been successful. Results of different types of matings are as follows : In view of the fact that the animals are all closely related, have been kept in the same room, and received similar treatment, there can be little doubt that the anomaly has a germinal basis which, through selection, has been mostly segregated in the D strain and practically eliminated from the B strain.

The effect of foreign skin on feather pattern in the common fowl (Gallus domesticus)

SummaryExperiments with skin grafting in the fowl have shown that a large measure of success is obtainable by means of a very simple technique. When a graft is placed on the back of a newly hatched chick the feathers subsequently developed conform very strictly in color and pattern to the type characteristic of the breed from which the graft was derived, except that occasionally some abnormally colored feathers are produced. These feathers are found to belong to two classes, one of which can be duplicated in unoperated birds, while the other is distinctive and represents a combination of the characteristics of donor and host. The data at hand do not justify anything more than a tentative hypothesis as to the exact mode of interaction in this case, but the fact that such an interaction does occur places the bird in line with some of the lower forms, and opens a new field for the study of regulatory processes in warm blooded animals.ZusammenfassungExperimente mit Haut, die Hühnern implantiert wurde, haben gezeigt, daß ein beträchtlicher Erfolg durch eine ganz einfache Technik erreichbar ist. Wenn ein Implantat auf den Rücken eines gerade ausgebrüteten Kükens gepflanzt wurde, entwickelten sich die Federn in der Folge in Farbe und Zeichnung ganz entsprechend dem charakteristischen Typus der Rasse, von der das Implantat genommen wurde, ausgenommen daß gelegentlich einige abnorm gefärbte Federn gebildet werden.Es ergab sich, daß diese Federn zwei Gruppen angehören. Die eine davon kann auch bei nicht operierten Vögeln vorkommen, während die andere besondere Merkmale zeigt und eine Kombination der Charaktere von Geber und Wirt darstellt. Das vorliegende Material rechtfertigt nicht mehr als eine versuchsweise Vermutung über die genauere Art der Wechselwirkung in diesem Falle. Aber die Tatsache, daß solch eine Wechselwirkung vorkommt, stellt den Vogel auf eine Linie mit einigen niedrigeren Formen und öffnet ein neues Feld für das Studium regulatorischer Prozesse bei Warmblütern.

Alcohol and the sex ratio in mice.

An animal heterozygous for a character produces two kinds of germ cells with respect to that character. Since these two classes of germ cells differ in their genetic potentialities, it is conceivable that they may also differ in their ability to react to varied environmental conditions. Critical tests of this question are difficult to devise, one of the best thus far being that introduced by Stockard 1 in his alcohol inhalation experiments. By use of Stockards method evidence has been obtained which indicates that when alcohol is thus introduced into the tissue of the fowl, germ cells are differentially affected according to their general vigor, 2 as well as on the basis of some of their genetic differences. 3 In the mouse, in which the male is presumably heterozygous for the sex chromosomes, Bluhm 4 found a much higher sex ratio after administering alcohol to the male parent by subcutaneous injections. The difference was attributed to a differential effect on the two classes of sperm cells. Bluhms work has been questioned 5 , 6 because of the low sex ratio in the controls (80 males: 100 females in a total of 965 young, as compared with a ratio of 122:100 among those sired by alcohol-injected fathers). The more recent data of Parkes 7 shows a wide seasonal variation in the sex ratio of mice which may help to explain the apparent discrepancy in Bluhms results. The present report covers three short experiments in which male mice were treated with alcohol fumes in the usual way. Cylindrical glass specimen jars of about 20 cm. diameter and 5.5 liters capacity were fitted with false bottoms of perforated paraffined wood supported on short metal legs.

Skin Transplantation as a Means of Analyzing Factors in Production and Growth of Feathers.

In most breeds of fowl there is a well marked sexual dimorphism in the color and structure of adult feathers. Experimental or pathological alteration of the endocrine balance has been shown 1 to produce striking reversals and modifications in these characters. Our problem has been to find a new method of attack which would yield further information on (a) the extent to which the output of a feather follicle is controlled by the endocrine relations which obtain at the time the feather is produced, and (b) the extent to which it is determined by characteristics which are inherent in the follicle itself. The procedure has been to transplant pieces of skin from one newly hatched chick to another and, some months later, to compare the feather production of the donor, the host and the skin originally transferred from the former to the latter. The technique is simple. Young chicks were found to take the anesthetic (ether) very satisfactorily. They recover quickly and do not suffer from infections when moderate care is exercised. The grafts are easily held in place by interrupted silk sutures, which usually fall out spontaneously, but may occasionally remain and serve as good landmarks over a period of several months. The general results obtained thus far may be briefly summarized. 1. The percentage of initial “takes” is high, but many grafts after having become well established are subsequently lost. Such grafts often appear entirely successful at first, and produce normal pin feathers or even fully developed feathers. The cause of these failures has not been studied, but the distribution of cases with reference to sex and breed suggests varying degrees of incompatibility between donor and host. This type of experiment promises to be very favorable for the study of differences in tissue reactions and “individuality differentials.”

Failure of Theelin and Thyroxin to Affect Plumage and Eye-Color of the Blackbird.

Evidence from a number of sources has made it apparent that sexual differences in the plumage of the common fowl (Gallus) are largely regulated by endocrine factors. In most breeds feathers of the male type are replaced, after administration of appropriate amounts of thyroxin, theelin or crude pituitary extract, by feathers resembling those of the female. Nevertheless, it is recognized that there are pronounced differences between breeds in their response to these prepared hormones. 1 For a time it seemed possible that the mechanism of differentiation in secondary sexual characters might be essentially the same in all avian species, the variations being only quantitative in character. Evidence seeming to point in this direction was obtained from a number of different orders and families. 2 More recently evidence of another sort has been accumulating. Males of the variegated South American plover, Vanellus chilensis, 3 the pigeon and the guinea fowl, in all of which the sexes are similar, have shown no plumage response to the injection of theelin, nor in the latter species to castration. The plumage of the female guinea fowl is likewise unaffected by ovariectomy. 4 The extensive studies of Keck 5 on the English sparrow have shown that the distinctive plumages of the male and female of this species are not influenced by castration or by gonad transplantation. These results indicate that the basis for the manifestation of sexual differences in plumage is not the same in all species. It apparently may differ radically within the same family (e. g., Fringillidae), 2 , 5 when genera and even species may show interesting deviations, 6 , 7 some of which suggest those found in breeds of poultry.

The Interaction of Genes in Development.

Since it has been shown that the transmission of most hereditary traits can best be explained on the theory of the gene, it is important to try to trace the relation between particular genes in the fertilized egg and the correlated somatic manifestations that appear during development. That such correlations do exist has been abundantly demonstrated, but just how the gene exerts its effect on the soma is still unknown. As a first step towards an analysis of this problem one may inquire into the interrelation between the genes themselves. Here there are two possibilities to be considered: (1) that the genes interact with each other to give the cell its structural and functional characteristics; (2) that each individual gene separately exerts its own specific influence. These alternatives may be illustrated by the following schemata, in which A and B represent the genes in a cell whose contribution to the soma may be either S or S′ (depending on such factors as topographical relations, stimuli, etc.). In (1) all the interaction between A and B is in the nucleus and N is the single resultant effect—a particular type of protoplasm. This would seem to correspond to a common conception among experimental biologists. In (2) A and B are more or less independent, n, n′ and n″ representing distinct elements in the total of cytoplasmic potentialities. In this case it is not the genes themselves, but certain of their secondary products that interact, so that while A ultimately affects both S and S′, B affects only one of them. The determination of which of these alternatives is in accord with the true situation is of considerable importance to the understanding of protoplasmic reactions in general.

Testicular Hormones and Sebright Plumage.

There are recognizable in the fowl 3 intergrading types of plumage, usually designated as hen-feathering, cock-feathering, and capon-feathering. The capon type, which does not occur normally in nature is, in effect, an exaggeration of the male form. It appears following the complete removal of testes or ovaries. Hen-feathering occurs in the presence of an adequate amount of functional ovarian tissue (native or grafted) in any individual, so far as known, without regard to breed or sex. It may also be induced by the injection of certain hormones, such as thyroxin, and occurs normally in males of certain breeds, notably Sebrights. Attempts to interpret these phenomena have led to 2 not wholly concordant views. One group of investigators 1 has postulated differences in testicular hormones, pointing out that the degree of cock-feathering varies in different races, but that in all races the male is less elaborately feathered than the corresponding capon. Others have questioned the differential effect of testicular hormones on plumage. Roxas 2 found that exchange of testes between hen-feathered and cock-feathered males had no effect on the plumage of either. Gallagher, Domm and Koch 3 have recently reported that purified testicular hormone, while having no effect on capons of cock-feathered strains, readily induces hen-feathering in Sebright capons. They interpret these findings as indicating merely somatic differences in response to the same hormone. Results following skin transplantation, 4 while for the most part supporting this contention, afford some indication of racial differences in the hormones themselves. The question is obviously still open, and calls for a more nearly quantitative analysis. The following experiments only partially meet this need. Three 5 1/2-months-old cockerels of Sebright type, full brothers, and very similar in appearance, were used for a gonadectomy test. In A the testes were left undisturbed, in B both were removed, and in C one was removed.

Different Potentialities of Male and Female Skin in Reeves Pheasants.

The extraordinary similarity of feathers produced by male and female fowls after gonadectomy has led to the idea that the skin in the 2 sexes is potentially the same. This inference seems to be supported by the effects of endocrine injections and the results of skin transplantation. It is further strengthened by the fact that, although between different races there is much variation in response to endocrines, the 2 sexes of any one race react rather consistently. Nevertheless, there are frequently detectable, though generally slight, differences between feathers produced by birds that were originally male and those that were originally female. This suggests that the genotype of the male and that of the female may condition slightly different responses when all other factors are held constant. A search for some form in which this problem could be approached more satisfactorily than in the common fowl revealed that the Reeves pheasant (Syrmaticus reevesi) is very satisfactory for the purpose. It is a species which breeds true to a standard type and has a plumage that is distinctive and varied, with none of the feathers of one sex duplicated by those of the other. The birds are rather expensive when purchased from dealers, but may be raised from eggs with relative ease. Homoplastic skin transplantation immediately after hatching was chosen as the method affording the most delicate and dependable test. The procedure has the disadvantage of requiring a wait of several months between the beginning of an experiment and attainment of the final result. It also involves certain losses due to incompatibility of tissues of donor and host. But in many cases no incompatibility is revealed and the grafted skin appears to behave normally in every respect, functioning as an integral part of the host.