INOCULATION OF ANIMALS HI 



contrasted with forms tending to grow in sarcinal packets, and 

 the Gram-staining forms were chiefly parasitic in habitat. 

 Looking at their results as a whole, Winslow and Rogers divide 

 the cocci into two great groups, the Paracoccaceae and the Meta- 

 coccaceae. The former comprise most of the forms derived from 

 the body, show a staphylococcal or streptococcal tendency, stain 

 by Gram, yield only moderate surface growths, form acid in 

 carbohydrates, and produce no pigment or a white or orange 

 colour. The latter come chiefly from air and water, often are 

 suviniform, decolorise by Gram, grow well on the surface of 

 media, do not ferment carbohydrates, and produce red or yellow 

 pigment. On similar lines, further subdivision of the groups 

 could be effected. It is manifest that important means of 

 differentiating allied bacteria may be available by the extended 

 application of this method. 



INOCULATION OF ANIMALS. l 



The animals generally chosen for inoculation are the mouse, 

 the rat, the guinea-pig, the rabbit, and the pigeon. Great caution 

 must be shown in drawing conclusions from isolated experiments 

 on rabbits, as these animals often manifest exceptional symptoms, 

 and are very easily killed. Dogs are, as a rule, rather insusceptible 

 to microbic disease, and the larger animals are too expensive for 

 ordinary laboratory purposes. In the case of the mouse and rat 

 the variety must be carefully noted, as there are differences in 

 >iisreptibility between the wild and tame varieties, and between 

 the white and In-own varieties of the latter. In the case of the 

 wild varieties, these must be kept in the laboratory for a week or 

 two before use, as in captivity they are apt to die from very slight 

 causes ; and, further, each individual should be kept in a separate 

 cage, as they show great tendencies to cannibalism. Of all the 

 ordinary animals the most susceptible to microbic disease is the 

 guinea-pig. Practically all inoculations are performed by means 

 of the hypodermic syringe. The best variety is made on the 

 ordinary model with metal mountings, asbestos washers, and 

 preferably furnished with platinum-indium needles. Before use, 

 the syringe and the needle are sterilised by boiling for five 

 minutes. The materials used for inoculation are cultures, animal 

 \ IK lat ions, or the juice of organs. If the bacteria already exist 

 in a fluid there is no difficulty. The syringe is most conveniently 

 filled out of a shallow conical test-glass, which ought previously 



1 Experiments on animals, of course, cannot, in Britain, be performed with- 

 out a licence granted by the Home Secretary. 



