ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 573 



The following is Dr. Ehrlich's method of procedure, which does 

 not present any technical difficulty, and does not require more than 

 an hour to make a dozen preparations. By means of a dissecting 

 needle a particle of expectorated matter, about the size of a pin's 

 head, is taken up and spread between two cover-glasses, * in two 

 exceedingly thin layers on each. The cover-glasses are then separated 

 by sliding one on the other, and left to dry protected from the dust. 

 After a few minutes they are dry, and the fixing of the albuminoids 

 and mucin is proceeded with. For this they can be warmed for an 

 hour at 100° or 120° C, or which is simpler, rapidly passed four or 

 five times through the flame of a spirit-lamp. To colour the prepara- 

 tions a saturated solution of phenylamine is to be made in distilled 

 water,f by shaking with the water the excess of aniline which floats 

 on it, and carefully filtering the whole. To the transparent liquid 

 thus obtained add, drop by drop, a saturated alcoholic solution of 

 fuchsine or methyl-violet until a slight opalescence is produced. The 

 preparation should not be immersed in the colouring bath, but be 

 placed in such a manner as to float on it, and to have the surface 

 which is covered with the tuberculous matter in contact with the 

 liquid. After a quarter to half an hour the staining is complete. 



If examined in this condition it is seen that the preparation is of 

 such an intense colour that it is impossible to distinguish its 

 elements, and Ehrlich happily thought of trying to decolorize it by 

 means of a strong acid ; colourless salts of aniline are then formed, 

 which are very soluble in water and disappear by washing with 

 distilled water. The bacteria, not being penetrated by the acids, 

 preserve their colour. In order to secure that they alone shall be 

 coloured, therefore, it is only necessary to immerse the cover- glasses 

 in nitric acid diluted with twice its volume of water. Nitrous vapours 

 are at once disengaged, and the preparation becomes absolutely 

 colourless in a few seconds. Under the Microscope the bacteria are 

 seen to be very clearly coloured red or violet ; but by reason of their 

 extreme delicacy they often escape the eye and require the most 

 accurate focussing. It is therefore better to study them in prepara- 

 tions which have been slightly coloured blue or green (when fuchsine 

 has been used for the first bath), or yellow (when methyl-violet has 

 been used). They are afterwards mounted in Canada balsam in the 

 usual way. 



The advantages of Ehrlich's method are summed up by Dr. E. 

 Van Ermengem as follows : — 1st. The aniline alters the form of the 

 histological elements much less than Koch's solution of potash. 

 2nd. The process is much quicker, and does not occupy more than an 

 hour. 3rd. Its principal advantage is to produce a more intense 

 staining of the bacteria, so that they appear larger, and can be 

 recognized with a lower power, even with 250 diameters. 



A question of the highest interest from a medical point of view 



* Ehrlich chooses cover-glasses whose thickness is appropriate to the 

 objectives to be employed; those from 0-10 to 0-12 mm. he considers the most 

 suitable. 



t The water dissolves about one part in thirty-one at the ordinary tempera- 

 ture, 12° C. 



