THE SELECTION OF ANIMALS 



157 



Cats are difficult to handle, and dogs are only slightly susceptible to most 

 of the organisms pathogenic to man. 



Frogs are occasionally used, but they are not very susceptible. 



Ground squirrels [Mus citullus ] are not only difficult to get in this country, 

 but they do not breed in captivity. 



Monkeys, and especially the anthropoid apes, have for some time been 

 little used for experimental purposes on account of the difficulty of obtain- 

 ing them, their initial cost, and the great care with which they have to be 

 tended in captivity. Nevertheless, the work of MetchnikofE and his pupils 

 on syphilis, [of the English Commission on tuberculosis, of Levaditi and 

 Landsteiner on acute polio-myelitis, etc. ] has shown the value of experiments 

 upon these animals in the investigation of human disease. [Macacus rhesus 

 is the most suitable for most purposes and at the same time the cheapest 

 monkey. ] 



SECTION II. THE KEEPING OF ANIMALS. 

 A. Small animals. 



Accommodation. The " small animal " house ought to be spacious, well 

 ventilated, floored with concrete or some similar impervious material and 

 have water laid on, so that it can be frequently washed down. 



Animals generally, and especially monkeys, rabbits, mice and rats, are 

 very susceptible to cold and damp ; the animal house must, therefore, be 

 kept dry, and facilities for warming it in winter should be provided. 



Cages, feeding, etc. The cages should, as far as possible, be made of metal. 

 It is a bad practice to place one cage on top of another, since fluids from the 

 upper cage may soil [and infect] the one beneath. If, from want of space, 

 it becomes absolutely necessary to place one cage on top of another there 

 must be a sheet of metal between them tilted and guttered, so that the 

 urines run off. The bottom of the cages should always be perforated. 



[A rectangular cage made entirely of fairly stout galvanized iron wire 

 and resting on a metal tray is both efficient and cheap (fig. 129). 



FIG. 129. Animal cage. The cage is raised on blocks from the tray. 



[The cage itself consists merely of a rectangular wire box of which one of 

 the two largest sides is hinged to form a lid allowing access to the interior. 

 A clasp must also be provided so that the top can be securely fastened down. 

 The cage is placed on a sheet of galvanized iron turned up to the extent of 

 1 or 1J in. all round to make it water-tight and measuring 1 inch larger in 



