Thomas M. Rivers

A Recently Described Virus Disease of Parrots and Parrakeets Differing from Psittacosis

The widespread outbreak of psittacosis in 1929 and 1930 incited experimental work that quickly resulted in the discovery of the fact that the disease is caused by an agent capable of traversing bacteria-tight filters. Thus the first filterable virus indigenous to parrots was found. Since Amazon parrots were believed to be the chief source of the infection, workers in Brazil sought for evidence of psittacosis in their country. Pacheco, Bier, and Meyer 1 - 2 - 3 - 4 encountered a disease in parrots that subsequently was shown to be induced by a filterable agent. According to their reports, the etiological agent passes Berkefeld N candles, is not cultivable on ordinary media, produces areas of necrosis in the liver and spleen in which are found acidophilic nuclear inclusions similar to those seen in herpes febrilis and Virus III infections, and is not pathogenic for pigeons, chickens, mice, guinea pigs, or monkeys. Moreover, these workers state that the clinical picture observed in infected birds is similar to that seen in avian psittacosis, and believe that the strict adaptation of the virus to the psittacidae accounts for the absence of human psittacosis in Brazil. Dr. Pacheco sent me some of his virus in order that its activities might be compared with those of a virus known to have caused psittacosis in human beings. This comparison has been made, and I can confirm the results of the experimental work reported by the Brazilian investigators. The virus is not retained by Berkefeld V and N candles, nor is it cultivable on ordinary media. Parrakeets are susceptible, while canaries, chickens, rats, mice, guinea pigs, and rabbits are insusceptible. Numerous acidophilic nuclear inclusions are found in the specific lesions. I do not agree, however, with the conclusions that the strict adaptation of the virus to parrots and parrakeets accounts for the absence of human psittacosis in Brazil.

Biotin in Elementary Bodies of Vaccinia.

Studies of the constituents of elementary bodies of vaccinia have shown that preparations purified by a standard technic exhibit uniformity in their chemical constitution and in their biological activity. 1 , 2 The virus appears exceedingly complex and therefore the view that respiratory catalysts, which are known to play an important rôle in bacterial metabolism, may function in the organization of elementary bodies of vaccinia is not untenable. With this in mind, we have examined elementary bodies for growth-factors. By means of a technic similar to that described by McDaniel, Woolley, and Peterson, 3 vaccine-virus has been shown to contain relatively large quantities of a substance capable of stimulating the growth of Clostridium butylicum in a synthetic medium. Moreover, partial hydrolysis of the virus by normal alkali or 4 normal sulfuric acid gives rise to increased quantities of this substance in active form, which, on the basis of studies similar to those made by Snell, Eakins, and Williams, 4 and others 5 , 6 on liver, yeast, egg-yolk, etc., we believe to be biotin. Two recognized technics exist for the microbiological assay of biotin. The first, employed by Snell, Eakins, and Williams 4 depends upon the growth-stimulus afforded by this substance to a standardized strain of yeast, while the second depends upon the stimulus afforded to the growth of Clostridium butylicum in a synthetic medium devoid of biotin. 3 Since the growth-requirements are simpler and somewhat better understood in the case of Clostridium butylicum, the second technic was adopted as affording the greatest guarantee against introducing with the material to be tested other physiologically active substances. Elementary bodies of vaccinia were prepared for biotin-assay in 3 ways: first, as dried virus, resuspended by physical agitation; second, by dissolving the dry virus in normal alkali with the aid of heat; and third, by refluxing the dry virus with 4 normal sulfuric acid for 30 minutes at 100°C.

Effect of Cathode Rays Upon Certain Bacteria

The following experiments, which are intended as preliminary steps in a study of some of the effects of cathode rays upon cells. provide data for a statistical analysis of the rate of killing of cultures of B. coli, of Staphylococcus aureus and of B. aertryke. The cathode rays have been obtained from a Coolidge type electron tube operated at a voltage of approximately 200 K.V. Small numbers of the organisms under investigation were evenly spread upon the surfaces of agar plates and known areas were exposed for different lengths of time to the electron stream. After incubation, counts were made of the numbers of colonies growing out in these areas and in similar standard areas shielded from radiation. The ratios of the bacterial colonies in these areas are survival ratios. A picture of the physical consequences of an electron absorption in a bacterium will be provided by remembering that whenever a fast moving electron is absorbed in matter, some of its energy will be emitted as X-rays but the major part will produce a large number of charged ions within a very small volume. In the present experiments this volume is probably less than 0.001 mm.3 and within it an absorbed electron gives rise to upwards of 10,000 ions. It is natural to attribute the destructive action of cathode rays to the chemical and physical changes resulting from this ionic shower. By estimating both the number of electrons which strike a bacterium in unit time and the absorption coefficient of these electrons in the bacterium, it is possible to analyse the observed survival ratios by the usual methods of probability theory. Such an analysis will show how many electrons may be stopped by a single bacterium before death results.