TEXT-BOOK OF BACTEKIOLOGY. 61 



on the sections or are even floated into the tissues, and we may 

 easily fall victims to deception if their somewhat superficial posi- 

 tion be not carefully noted. 



Some faults of investigation arise from faulty staining-. 



Very frequently in Gram's process, and also in other processes, 

 the coloring matter of badly-filtered solutions is deposited upon 

 the preparation, usually in the form of very small, roundish bodies, 

 which lie together in masses and are apt to be mistaken for micro- 

 cocci. The irregular forms of the particles, their peculiar shining 

 appearance, and 'the want of order in their distribution over the 

 different parts of the tissue will suffice to prove that they are not 

 what they seem. 



The influence of the iodine solution on bacterial preparations 

 sometimes shows itself in a very remarkable manner. The rod- 

 bacteria break up into a bead-like row of granules, reminding one 

 of a chain of globular bacteria. The more strongly-acting acids 

 also produce such appearances now and then, and in fact this 

 has led to the mistaking of indubitable bacilli for micrococci. Yet 

 the true state of the case is nearly always recognizable by the 

 occurrence of unaltered rods in the preparation, as also by the 

 presence of intermediate, only partly-altered, forms. 



Some faults of investigation lie, not in any defect of the object, 

 but in the observer, who wrongly interprets what he rightly sees. 



In making preparations of blood to search for bacteria, we place 

 a small quantity of the fluid on a cover-glass, lay a second glass 

 upon it, and then pull the two apart again. This proceeding does 

 not fail to produce its influence on certain ingredients of the blood. 



By the attraction of the two glasses some white blood-cells are 

 burst, their nuclei are crushed, and then drawn apart when the 

 glasses are separated. As these consist of nucleus substance, they 

 are naturally stained by the anilin. In this manner one gets the 

 strange-looking, comet-like figures in the picture thick heads with 

 long tails; in others, all remains of nucleus form are destroyed and 

 one sees only long stretched threads, which have more than once 

 been taken for the mycelia of blue-mould fungi. Lastly, such a 

 thread will sometimes break up into pieces or resolve itself into a 

 row of little granules, and then we see "bacilli" and "cocci," but 

 with a little attention and experience we learn to be on our guard 

 against such mistakes. The list of the commonest faults of investi- 

 gation will be closed by warning against one which is made by 

 almost every beginner. 



There is in tissue a particular kind of cells, the so-called plasma- 

 cells or granule-cells, whose behavior under the influence of anilin 



