Howard Winet

Geotaxis in Protozoa I. A propulsion—gravity model for tetrahymena (Ciliata)☆

Abstract A propulsion-based model for negative geotaxis of ciliated protozoa is presented which views geotaxic reorientation as the unbalancing of gyrational torque by a sedimentation torque. The balanced gyrational torque results from the location of the propulsive center of effort forward of the body center of mass. When gravity is ignored, the propulsive forces generating the gyrational moments may be confined to an envelope surrounding the cell. The effect of gravity is to induce sedimentation of the body-plus-envelope system. Viscous resistance to this sedimentation at the envelope “surface” is transmitted to the beating cilia whose net constant energy output must now deal with a new source of dissipation (not “present” when gravity was ignored) which is maximal in the downswing portion of the gyration cycle. In such a manner sedimentation resistance acts as a counter torque to the downswing gyrational moment of force and an enhancing torque to the upswing moment thereby generating a net upward reorientation of the gyrational axis. Upon addition of the translational component of propulsion, the negative geotaxis behavior pattern is completed. The forward location of the center of effort which provides the basic validity indicator for the model is verified by observations from the ciliate Tetrahymena .

Monitoring the degradation process of biopolymers by ultrasonic longitudinal wave pulse-echo technique

A non-destructive ultrasonic longitudinal wave pulse-echo technique was utilized to monitor the degradation process of three biodegradable polymers: poly(glycolic acid) (PGA), poly(L-lactic acid) (PLLA) and 50:50 poly(D,L-lactide-co-glycolide) (PDLLG). The degradation processes of PGA and PLLA, which have different molecular structure, were also studied by differential scanning calorimetry (DSC). The degradation processes of PDLLG specimens prepared by different methods were characterized by the ultrasonic wave technique and gel permeation chromatography (GPC). The resulting acoustic and thermal properties indicate that PLLA and PGA exhibit distinctly different degradation behavior, whereas the acoustic properties and molecular weight of PDLLG are sensitive with preparation methods. The present study demonstrates that ultrasonic wave technique provides a powerful tool in detecting the property changes of biodegradable polymers prepared with different manufacturing process and that the degradation behavior of biodegradable polymers can be closely monitored by ultrasonic technique.

SECRETORY ACTIVITY OF THE ORAL APPARATUS OF CILIATES: TRAILS OF ADHERENT PARTICLES LEFT BY PARAMECIUM MULTIMICRONUCLEATUM AND TETRAHYMENA PYRIFORMIS*

T r a i l s of adherent p a r t i c l e s w e r e f i r s t s e e n by us in motion ‘hpportmd bY ONR contract Nonr 233(65) and NIH grant No. 6462.

Skeletal muscle contractions uncoupled from gravitational loading directly increase cortical bone blood flow rates in vivo

The direct and indirect effects of muscle contraction on bone microcirculation and fluid flow are neither well documented nor explained. However, skeletal muscle contractions may affect the acquisition and maintenance of bone via stimulation of bone circulatory and interstitial fluid flow parameters. The purposes of this study were to assess the effects of transcutaneous electrical neuromuscular stimulation (TENS)‐induced muscle contractions on cortical bone blood flow and bone mineral content, and to demonstrate that alterations in blood flow could occur independently of mechanical loading and systemic circulatory mechanisms. Bone chamber implants were used in a rabbit model to observe real‐time blood flow rates and TENS‐induced muscle contractions. Video recording of fluorescent microspheres injected into the blood circulation was used to calculate changes in cortical blood flow rates. TENS‐induced repetitive muscle contractions uncoupled from mechanical loading instantaneously increased cortical microcirculatory flow, directly increased bone blood flow rates by 130%, and significantly increased bone mineral content over 7 weeks. Heart rates and blood pressure did not significantly increase due to TENS treatment. Our findings suggest that muscle contraction therapies have potential clinical applications for improving blood flow to cortical bone in the appendicular skeleton.

Letter to the Editor: Not the Last Word: Rethinking the Resident Research Requirement

I am just a scientist, so I generally work with data, not patients. But for more than 15 years, I enjoyed interacting with orthopaedic residents as they completed their research experience. I never felt that I was turning them into scientists, and certainly not basic scientists. My main function was to help them learn how to critically read a research paper so they could logically evaluate its value for their practice. Medicine is a truth profession in which clients expect a truth—their successful treatment—to be achieved. Empirical science applies epidemiological techniques to observations and yields what Plato called ‘‘knowledge of the giants’’ [1] or in other words, correlations good enough to support actions. Basic or causal science was once thought to be a path to ‘‘knowledge of the Gods’’ [1]—ultimate truths. That goal is now deemed beyond us scientists. Our conclusions are transitory—we were barred from asserting ‘‘proofs’’ by theoretical physicist Werner Heisenberg in 1927. Our data, however, and particularly the integrity of those data, define our worth. We are uncertain about all else. We must fail in order to grow as scientists because we are expected to learn from our failures. There is no doctrinaire scientific method, but there is peer review of any method that is different. Some of my residents have published papers, but rarely were they more than just nice conversation at cocktail parties. Perhaps you, and Drs. Chehade, Pinney, and Black (the commentators who had the ‘‘last words’’ in your column) have published papers that provide considerable contributions to orthopaedic research. I humbly congratulate you on your successes. My satisfaction, however, is driven by hearing one of my residents challenge a presenter’s sample size or his/her claim that (s)he has ‘‘found THE mechanism for’’ something, especially if the speaker fails to present alternatives or state problems with his own hypothesis. Writing an NIH grant, as you propose in your column, may be a useful exercise. However, having taught an ethics course for 10 years, I can appreciate how an ethical problem could arise when a principal investigator uses the resident as a technician or to perform research work without compensation or attribution. In other words, to exploit the resident. This is a dark side of research that must be acknowledged when evaluating any research experience program.