The classification of the cell-granules of the blood according to their various chemical affinities which was drawn up by this method is accepted to-day as the most valuable, and the only practical means of grouping the leucocytes. From the first Ehrlich has insisted, =that different kinds of cells possess different granules=, distinguished not only by their tinctorial properties, but also by their various reactions to solvents.
It is in this connection indeed, that Altmann's method, consisting of a complicated hardening process, and the use of a single, always similar stain, constitutes a retrograde step, in as much as it tends to obscure the principle of the specificity of each kind of granulation.
A further disadvantage of Altmann's hardening method lies in the circumstance, that the cell proteids are precipitated by it in a spherical form, and stain in the subsequent treatment. Hence it is extremely difficult to distinguish what is preformed, and what is artefact. Since A. Fischer's publication, where the formation of granule-like precipitates under the influence of various reagents is experimentally demonstrated, grave doubts as to the reality of Altmann's forms have been raised from various quarters. Ehrlich's dry process, on the contrary, is entirely free from error. Granules cannot be artificially produced, by desiccation, and the stained appearances correspond precisely to what is seen in fresh living blood. The greatest value of the dry method is that the =chemical nature= of the single granules remains unchanged, so that attempts at differentiation are made on a nearly unaltered object[22].
Another means of studying the nature of the granules depends on the principle of =vital staining=. The "vital methylene blue staining" (Ehrlich) that has since become so important, especially in neurology, led to the first attempts at staining the granules in living animals. One of the first publications on this subject is that of O. Schultze, who placed the larvæ of frogs in dilute methylene blue solution, and after a short period found the granules of the stomach, the red blood corpuscles and other cells stained blue. This method, however, cannot pass as entirely free from error, as Ehrlich frequently found that when the experiment lasts some time the methylene blue often forms granular precipitates that may be confused with the granules. Teichmann directs a detailed analysis to this point, and regards most of the granules described by Schultze as artificial products.