BLOOD-SERUM. Ill 



peeled, sliced into discs of about 1 cm. in thickness, 

 and placed in small glass dishes provided with covers, 

 similar to the ordinary crystallizing dishes. The dish 

 and its contents are then sterilized by steam in the 

 usual way. By this plan a relatively large area for cul- 

 tivation is obtained. 



Potatoes may also be boiled, or steamed, and mashed, 

 and the mass placed in covered dishes, test-tubes, or 

 flasks, and sterilized. By this method one obtains in 

 the mass a mean of the composition of the several pota- 

 toes, or bits of potatoes, used in making it, an advan- 

 tage where uniformity is desired. 



Care must be given to the sterilization of potatoes, 

 because they always have adhering to them the organ- 

 isms commonly found in the ground, the spores of which 

 are among the most resistant known. The so-called 

 potato bacillus is one of this group ; it is an organism 

 which is not infrequently more or less of an obstacle 

 to the work of the beginner. 



BLOOD SERUM. For ordinary routine work blood 

 serum may be obtained from either the slaughter houses 

 or the antitoxin manufacturers. When from the for- 

 mer the blood that streams from the severed vessels of 

 the throat of the slaughtered animal is collected under 

 as cleanly conditions as possible in large, clean glass 

 museum jars. These are then, with the covers placed 

 upon them, set aside in an ice chest until coagulation is 

 complete. The serum may then be decanted or pipet- 

 ted off into flasks and thus transported to the labora- 

 tory to be sterilized by the method given below. 



In many localities it is possible to purchase at a small 

 cost normal horse serum in bulk from firms engaged in 



