202 SCIENCE PROGRESS 



reaction or what not, is watched through the microscope : it 

 is quite easy, for instance, to demonstrate in this way that 

 the nucleus gives the colour tests which are characteristic of 

 the proteins. Of recent years methods have been devised 

 for the micro-chemical detection of phosphorus and of iron, 

 and the presence of both these elements in the nucleus can 

 thus be shown. The existence of iron in the nucleus in 

 organic combination is not devoid of practical interest, for 

 there is no doubt that the normal supply of iron for the 

 making good of effete blood-pigment in the adult, and the 

 supply of iron wanted by the embryo for making haemoglobin 

 (of which there is none in the original ovum), is derived from 

 the iron-containing nucleo-proteins, or as Bunge terms them 

 hcematogens. It is perhaps hardly necessary to mention in 

 passing that Bunge's hasmatogen is a very different thing from 

 certain patent medicines sold under the same name. 



Macallum of Toronto is the most notable living exponent 

 of the art of micro-chemistry, and has followed with infinite 

 patience the distribution of various elements or compounds 

 in situ in the different tissues. Among methods he has recently 

 devised, for instance, is one for the detection of potassium 

 by means of cobalt nitrite, and another for the detection of 

 chlorides by means of silver nitrate. Both potassium and 

 chlorine, however, curiously enough, are absent from the 

 nucleus of all cells, or at any rate cannot be detected by such 

 means. In a sense, too, every staining reaction is a chemical 

 reaction. Many dyes, used either for staining fabrics or 

 histological specimens, are taken up by the process known 

 as adsorption ; this is something midway between chemical 

 combination and mere mechanical admixture. But in other 

 cases the facts are not explicable by the adsorption hypothesis, 

 and no doubt in these, or in some of them, a true chemical 

 compound is formed between the dye and the material which 

 is dyed. In the future, when our knowledge of the chemistry 

 of dyes, as well as of the organic substances in living tissues, 

 is more complete, it will be possible to state the nature of the 

 compounds which are formed. But even at the present day 

 we are not absolutely ignorant on such points, and perhaps 

 it is in relation to the aniline dyes that our knowledge, such 

 as it is, is greatest. Some of these stains are neutral in 

 reaction, some acid, and some basic ; and it is the custom to 



