200 THE ACTION OF THE LIVING CELL 



reason breeders of other species of animals have not 

 seen fit to employ the same care in the treatment of 

 their charges. Indeed, such breeders are inclined to 

 scoff at the pampering which the white rat receives in 

 the larger laboratories. They argue that the rat is a 

 hardy animal naturally acclimated to life under con- 

 ditions usually regarded as unhygienic for other spe- 

 cies. While this is true, the scoffers forget that the rat 

 breeders would not indulge in the care and attendant 

 effort which they expend on their animals unless it 

 had been found to pay, not only financially, but also 

 in insuring the production of a constant supply of 

 hardy animals suitable for purposes of experimenta- 

 tion. 



It may not be amiss to suggest that the ill health all 

 too common amongst humans in congested districts 

 may in part be due to the same cause as that found 

 in the case of caged animals. Everyone has heard the 

 virtues of "country air" extolled, and I believe that 

 most of us are ready to admit that there is something 

 invigorating about country air that is lacking in the 

 city. By analogy with the animal experiments dis- 

 cussed above, it seems probable that in densely popu- 

 lated areas the atmosphere must contain a certain 

 amount of human cytost which is lacking in the coun- 

 try air. On this assumption the invigorating nature 

 of extra-urban atmosphere lies in its comparative free- 

 dom from cytost. This inference, of course, is only 

 speculation which cannot be proved by direct experi- 

 ment, but several facts of human experience appear 

 to testify to its correctness. Thus, it has long been 

 recognized that patients suffering from respiratory 

 infections recover more rapidly outside the larger 



