148 LABORATORY EXERCISES IN BACTERIOLOGY. 



soon as possible after death in order to prevent the appearance of the organisms of 

 putrefaction as a source of error and confusion; and wherever an early operation is 

 impracticable the cadaver should be kept on ice or in a refrigerated room to avoid 

 the same trouble. Inoculations should be made from all special points of involvement, 

 and from the blood of the heart, spleen, any exudates in the tissues or body-cavities, 

 the liver and the kidneys as a matter of routine. In obtaining the material from 

 such sources the same precautions to prevent contamination should be observed as 

 directed above when dealing with tissues removed surgically, penetration into the 

 interior of cavities and through the capsules of organs being accomplished by a hot 

 blade, and the material removed by sterile syringe, needle, or other appliance. In- 

 stead of an ordinary platinum needle the heavy platinum harpoon of Nuttall, in a 

 metal or glass handle, is of advantage in that it is not easily bent in penetration into 

 firm tissue. 



After inoculations have been made from the various sources desired, not before, 

 films should be smeared upon glass covers or slides from each examined part for micro- 

 scopic study. 



CULTIVATION OF INOCULATED MEDIA. 



The conditions for growth and multiplication of bacteria are the availability 

 of a proper nutrient and moisture, and the presence of a suitable temperature and atmos- 

 phere. In addition, quiet and absence of extremes of light or darkness should be included. 

 These conditions are sought to be obtained in the measures taken for the successful 

 cultivation of the germs in the laboratory. 



1. Nutrient. Sufficient has been said concerning this feature in the consideration 

 of the various media to indicate that the important elements of nutrition carbon, 

 hydrogen, oxygen, and nitrogen, as well as traces of other elements (as iron, sulphur, 

 phosphorus, etc.) are obtainable from the media themselves. There are numerous 

 organisms which grow upon much more simple preparations than the ones described, 

 as upon solutions of salts ; and there are probably a number for whose artificial culti- 

 vation the media thus far devised have not approached sufficiently the material afforded 

 by the living body. The last are truly obligate parasites. The intricate changes 

 which are accomplished by the organisms in their appropriation of nutrition and 

 growth in these laboratory cultures are, of course, but poorly understood. They 

 are mainly reduction processes, oxidations, and hydrations. 



2. Moisture. The moisture present in a medium is an essential element; experi- 

 ments in which it has been purposely diminished show that its loss exerts a disturbing 

 influence upon the development of the organisms, growth being most vigorous when 

 seventy or more per cent, of water is present in the composition of the medium, and 

 practically disappearing when it has been reduced as low as forty per cent. Upon 

 this depends the success of practical preservation of foods and other organic sub- 

 stances by drying. The drying of. the medium does not necessarily destroy the vital 

 possibilities of the bacteria in the substance, even though there be no spores to account 

 for the persistence ; and after months of drying it is often possible to see profuse growth 

 appearing after the addition of water or bouillon to a dried culture. In order to pre- 

 vent the loss of moisture from the culture tubes, particularly those in the incubator, 

 the warmth of which would otherwise much hasten desiccation, a number of devices 

 are occasionally resorted to. The tubes may be capped with rubber covers or closed 

 with rubber stoppers (as for preservation of the uninoculated nutrient media) ; or 

 the atmosphere of the incubator (or of whatever other inclosure in which the cultures 



