234 BACTERIOLOGY 



progress of the disease by its effect upon the physical condi- 

 tion of the animal, viz., upon the nutritive processes, as 

 evidenced by fluctuation in weight, and upon the body- 

 temperature. For this purpose the animal is to be weighed 

 daily, always at about the same hour and always about mid- 

 way between the hours of feeding; at the same time its 

 temperature, as indicated by a thermometer placed in the 

 rectum, is to be recorded.' By comparison of these daily 

 observations the observer is aided in determining the course 

 the infection is taking. 



Too much stress must not, however, be laid upon moderate 

 and sudden daily fluctuations in either temperature or 

 weight, as it is a common observation that presumably 

 normal animals when confined in cages and fed regularly 

 often present very striking temporary gains and losses in 

 weight, often amounting to 50 or 100 grams in twenty-four 

 hours, even in animals whose total weight may not exceed 

 500 or 600 grams; similarly unexplainable rises and falls 

 of temperature, often as much as a degree from one day to 

 another, are seen. Such fluctuations have apparently no 

 bearing upon the general condition of the animal, but arp 

 probably due to transient causes, such as overfeeding or 

 scarcity of food, improper feeding, lack of exercise, excite- 

 ment, fright, etc. 



The accompanying charts (Figs. 47, 48, 49, 50) will serve 

 to illustrate some of these points. The animals, two rabbits 

 and two guinea-pigs, were taken at random from among 

 stock animals and placed each in a clean cage, the kind used 

 for animals under experiment, and kept under as good 



1 The thermometer must be inserted into the rectum beyond the grasp 

 of the sphincter, otherwise pressure upon its bulb by contraction of this 

 muscle may force up the mercurial column to a point higher than that 

 resulting from the actual body-temperature. 



