284 LABORATORY EXERCISES IN BACTERIOLOGY. 



sclera is incised and through the opening thus made the infection introduced by syringe 

 or on a small sterilized forceps. 



Inoculations into the cerebro-spinal area are made after performance of a definite 

 surgical opening of the cranium by trephine or chisel, the operation being performed 

 somewhat to one side of the sagittal line in order to avoid the longitudinal sinus. 

 Through this opening a sterile forceps grasps the dura mater and draws it slightly 

 upward in a small fold as well as may be done ; through the fold or the adjacent 

 tense part of the membrane the needle of the syringe is passed into the arachnoid 

 space, into which the fluid and its contained bacteria are forced slowly; the trephine 

 opening is covered by the replacement of the reflected overlying tissues and the 

 external wound dressed as in ordinary surgery. 



In inhalation inoculations the animal is placed in a small closed chamber, into 

 the atmosphere of which the fluid in which the bacteria are suspended is vaporized 

 mechanically, and the animal left in the chamber for a time to breathe the air con- 

 taminated with the infection. 



Alimentary inoculation is accomplished by mixing some of the culture with the 

 food and then allowing the animal to feed upon it. Occasionally enemata containing 

 the infected matter are thrown into the lower intestinal tract. 



After inoculation has been performed the experiment animals should receive 

 regular and frequent observation as to the condition of the inoculation site, the presence 

 of other apparent structural alterations, and the presence of any general or special 

 symptoms. The temperature of the animal should be taken by rectum at regular 

 intervals and charted, the movements, attitude, appetite, excretions, and the general 

 appearance and habits of the animal watched and recorded; and the occurrence of 

 spasms, lethargy, or other appreciated phenomena should be made a matter for record. 

 If one be studying an organism derived from a diseased individual, all these peculiarities 

 are to be carefully compared with the symptoms observed in the original disease and 

 their similarity or identity established; but it is to be recollected that the difference 

 in the experiment animal from the originally diseased individual and the mode of 

 artificial inoculation may make considerable difference in the clinical pictures of the 

 two cases. 



Disease production by bacteria may be brought about through several possible 

 separate or combined influences. They may (a) cause irritation by their presence 

 or their active movements in the tissues in some locality (or if numerous points of 

 irritation be induced, a more or less general inflammatory condition may be present) ; 

 (6) they may act untowardly by the abstraction of important elements, as oxygen, 

 from the system (either the bacteria or their products) ; (c) when in great numbers 

 in some passageway, as a small vessel, they may cause its obstruction and thus perhaps 

 interfere with nutrition or some other important function ; and (d) they may elaborate 

 or cause the formation from the body-elements of principles which are poisonous to 

 the host (vide Lesson VII, section Alkaloidal Products). The most important of 

 these modes of operation is the last, to which are due principally the general symptoms 

 of disease, as well as the various degenerative changes of the tissues; to the first of 

 these influences are due in large measure the inflammatory changes met about the 

 site of inoculation. 



After the death of the animal (which may be killed upon definite development 

 of evidence of the presence of disease) a careful autopsy should be made in order to 

 establish the alterations which have been produced in the tissues and to render certain 

 that the organisms inoculated have been the true or probable cause of the disease 



