Methods of Determination of Pathogenic Microbes. 143 



or two drops of the liquid are then expelled and 

 may be seen diffusing themselves in the transparent 

 media. 



6. Intra- cranial inoculations.— It is necessary here, 

 in the first place, to trephine the cranium, an opera- 

 tion which necessitates a variety of instruments. In 

 small animals, however, the operation can be very 

 simply performed. The animal being made fast, an 

 incision is made in the skin over the frontal bone out- 

 side of the median line, the periosteum is crucially 

 divided and, with the point of a strong bistoury held 

 vertical to the surface of the bone, a small opening is 

 made by rotating the instrument upon itself. 



When the opening is considered to be of sufficient 

 size the canula, thoroughly sterilized, is introduced 

 under the cerebral envelopes and a few drops of the 

 liquid injected. 



Inoculations may also be made into the various 

 serous cavities, the trachea, muscles, etc., but the 

 technique of these operations needs no special de- 

 scription. 



Besides these contagions by inoculation, an organ- 

 ism may also be artificially infected by the methods 

 of ingestion or inhalation of virulent products. These 

 methods o-ive results relutivelv less certain. 



Collection of virulent products. — Pathological prod- 

 ucts can be collected either from diseased animals or 

 from their cadavers. 



On diseased animals the process differs according as 

 it is desired to collect a liquid (blood, pus, etc.) or a 

 solid particle. Great precautions should always be 

 taken in order to avoid the common germs which 

 surround us. After the region hns been shaved it 



OP THE 



