54 



PHYSIOLOGY or NUTRITION 



Hours after Milking 



4 



9 



24 



Bacteria per cc. 

 34,ooo 

 100,000 

 4,000,000 



The intestinal tract of man is densely populated with bacteria, which fre- 

 quently cause decomposition of foods in the intestine. We are thus not only 

 externally surrounded by bacteria, but are even internally infested with them. 

 This seems to explain why these organisms appear so promptly in all kinds of 

 organic material that they decompose. 



§5. Sterilization and Disinfection.^ — In view of the fact that microorganisms 

 are so universally present, all objects used in handling them must be absolutely 

 free from spores or germs of any kind, especially if pure cultures of a certain 

 species are desired. This is accomplished by sterilization. Such small objects 



FiG- 33- — Dry-air sterilizer heated by gas. 



as knives, scissors, glass rods, forceps, sUdes and cover glasses, platinum needles, 

 etc., may be sterilized by heating in a gas or alcohol flame. Platinum instru- 

 ments may be brought to a red heat but for other objects a few moments in the 

 flame suffices, so that germs clinging to the surface may be destroyed. A dry- 

 ing oven, or dry-air sterilizer, is used for the sterilization of larger objects (Fig. 33) . 

 This is usually equipped with double walls, the products of combustion from the 

 gas flame below passing between the two walls and thus rendering the heating 

 uniform." 



1 Abel, Rudolf V. L., Taschenbuch fur den baktenologischen Praktikantcn. [.\bers Laboratory hand- 

 book of bacteriology. Tr. from loth German ed. by M. H. Gordon. London, 1907 ] Kuster Ernst 

 Anleitung zur Kultur der Mikroarganismen f(ir den Gebrauch in zoologischcn. botanischen, medizi'nischen 

 tlnd landwirtschaftlichen Laboratorien. Leipzig and Berlin, 1907. 



' For most satisfactory work the oven should have an automatic temperature-regulator, 

 various forms of which are available for gas. Electrically heated, automatically regulated 

 ovens are also obtainable, some of which are so well insulated that but little heat escapes to the 

 exterior. — Ed. 



