INTRODUCTION 



tion of intermittent exposures before or after infection. Are the 

 animals cold acclimatized? One must ask how acclimatization is 

 determined. Does it merely mean exposure for some time prior to 

 infection, or is there some measurement employed that proves the 

 animals are cold tolerant? Of greatest importance, in my judgment, 

 are detailed descriptions of experimental conditions of the exposure 

 to cold. Are the animals housed separately or in groups? Is bedding 

 material provided? If they are singly housed, how much space is 

 available? What is the velocity of air movement around the animals? 

 Is relative humidity controlled, and if so, at what saturation? Are 

 food and water continuously available?! confess as much ignorance 

 about these matters as most anyone, yet a few preliminary experi- 

 ments have clearly indicated that these factors cannot be ignored. 

 Another consideration is illumination. Continuous dark, continuous 

 light, or intermittent and erratic light are all to be avoided. Physi- 

 ologists concerned with biological clocks or with periodicity in 

 higher organisms have established beyond reasonable doubt that 

 carbohydrate reserves, body temperature, endocrine secretion, 

 eosinophile counts, and many others are all subject to highly sig- 

 nificant variations from one time of day to another (Halberg, 1960). 

 Some of these changes may be correlated with light, while others 

 may show free- running periods not directly associated withdetect- 

 able environmental phenomena. Space in which the animal is housed, 

 cubic volume as well as area, may contribute in unsuspected degree 

 to certain responses under investigation. The exigencies of space 

 travel is making this an important object of study. Research in in- 

 fectious diseases may be able to add something of significance to 

 this work. 



As moderator for our final session, it is a particular pleasure 

 for me to welcome a very close friend of many years. We took 

 several graduate courses together, our doctoral research was 

 carried out in laboratories opening into the same basement corridor, 

 we shared our frustrations and successes with one another, and we 

 walked across the platform the same hot June night in Texas more 

 years ago than either of us cares to admit to receive our Ph. D. 

 degrees. Dr. R, B. Mitchell has beenthe author of numerous scien- 

 tific papers, and is now continuing his service to science through 

 primarily administrative channels as Chief of the Department of 

 Medical Sciences, School of Aerospace Medicine. 



