PRESENCE IN TISSUES. 315 



reliable tests, however, have demonstrated the error of 

 this opinion. 



It grows at any temperature between 20 C. and 38 

 C., though more favorably at the latter point. 



It is very sensitive to high temperatures, being killed 

 by an exposure often minutes to 60 C., and in a much 

 shorter time to slightly higher temperatures. 



Owing to a tendency toward retraction of its proto- 

 plasm from the cell envelope and the consequent pro- 

 duction of vacuoles in the bacilli, the staining of this 

 organism is usually more or less irregular. At some 

 points in a single cell marked differences in the intensity 

 of the staining will be seen, and here and there areas 

 quite free from color can commonly be detected. These 

 colorless portions are often so cleanly cut in outline as 

 to look as if they had been punched out with a sharp 

 instrument. (Diagram matically represented in Fig. 63.) 



FIG. 63. 



Diagrammatic representation of retraction of protoplasm, with production of 

 pale points, in the bacillus typhi abdominalis. 



PRESENCE IN TISSUES. It is not easy to demonstrate 

 this organism in tissues unless it is present in large 

 numbers. The manipulations to which the sections are 

 subjected in being mounted often rob the bacilli of their 

 staining, and render them invisible, or nearly so. If, 

 however, sections be stained in the carbolic-fuchsin solu- 

 tion, either at the ordinary temperature of the room or 



