EXPERIMENTATION UPON ANIMALS. 225 



The animal should be tacked to a board if small, or 

 tied, by cords fastened to the legs, to the corners of a 

 table if large, and should be dissected with sterile knives 

 and scissors. When a culture is to be made from the 

 interior of an organ — say the spleen — it should be incised 

 deeply with a sterile knife and the culture made from 

 its centre. 



Fragments intended for subsequent microscopical ex- 

 amination should be cut very small (cubes of 1 can,), 

 placed in absolute alcohol for a few hours, then trans- 

 ferred to weaker alcohol, 80-90 per cent., for preserva- 

 tion. The technique of imbedding and staining the tis- 

 sues can be found in almost any reliable text-book on 

 pathology or on the special subject of microscopical 

 technique. 



Collodion capsules are quite frequently employed for 

 the purpose of growing bacteria in a confined position in 

 the body of an animal, where they can freely receive and 

 utilize the body-juices without being subjected to the 

 action of the phagocytes. In such capsules the bacteria 

 usually grow plentifully, and not rarely their virulence 

 is greatly increased. 



The capsules can be made of any size, though they are 

 probably most easily handled when of about 5-10 c.cm. 

 capacity. Their size is always an objection to their use, 

 because of the disturbance they cause in the animal's 

 abdominal cavity when introduced. 



The capsules are made by carefully coating the outside 

 of the lower part of a test-tube with collodion until a suf- 

 ficiently thick homogeneous layer is formed. During 

 the coating process the tube must be twirled alternately 

 within and without the collodion, so that it is equally 

 distributed upon its surface. When the desired thick- 

 ness is attained, and the collodion is sufficiently firm, the 

 tube is plunged under water and the hardening process 

 checked. 



A cut is next made around the upper edge of the col- 

 lodion film, and it is removed by carefully turning it 



15 



