I.— PHYSIOLOGY. 173 



This ' 307 ' Las a remarkable action on trypanosomes in laboratory 

 animals, being 300 times more effective than atoxyl. Its discovery has 

 also opened a new era in therapeutics, since it represents the first chemical 

 substance which when administered to man or animals in an infected 

 trypanosome district gives a complete immunity to the disease for several 

 months : it does not necessarily prevent trypanosome infection, but it 

 prevents the effects of the disease. There is much in these experiments 

 that suggests that we are on the fringe of a new pathology, and that our 

 present crude methods of preparing anti-bodies in the future will be 

 replaced by those of the organic and colloid chemist. 



In man ' 205 ' has not done all that was expected of it ; it invariably 

 benefits those that show infection and enlargement of glands, that is 

 during the early stages of the disease, and its value is also assured even 

 when the nervous system is affected. If care is taken in the treatment 

 and a series of injections given at not too frequent intervals to prevent 

 the parasite acquiring a tolerance, and if the patient is kept under 

 observation for a prolonged period of time, the happiest issue may be 

 anticipated. ' 307 ' is much less valuable on n'gana in animals. 



I have already referred to the disappointing results of research dealing 

 with chemical constitution in its relation to pharmacological action, but 

 it may be well to consider whether there is anything in common between 

 the various substances noted and their effects on protozoa. It must be 

 evident at once that with such widely different substances it cannot be 

 the form of the molecule which is important so much as its side-chains or 

 physical properties, although a large molecularweight appears to be an 

 advantage. Many of the dyes, like flavine, fuchsin, and methyl violet, 

 have two amino radicles in the para position, relative to the carbon 

 atoms uniting the nuclei. The azo-dyes and the innumerable derivatives 

 from them, which have been examined by NicoUe and Mesnil, present no 

 common features with those of the triphenyl methane group. Amino 

 groups appear to be an important factor, but it is the position of these in 

 the rings, even more than the character of the radicle, which determines 

 the effect. The study of the complex butterfly-like compounds of sub- 

 stituted naphthalenes, such as Fourneau's ' 307,' instead of simplifying our 

 conception of the relationship between constitution and action rather 

 increases the difficulties. In such compounds slight changes like desul- 

 phonation or demethylation entirely alter the therapeutic effect. These 

 few examples are sufficient to exemplify the fact that the synthesis of new 

 molecules in the hope of conforming with some pre-determined action ia 

 as yet far removed from practical science. 



Bacterial Infections. 



Tuberculosis is another problem of vast importance in South Africa, 

 not only on account of its prevalence amongst susceptible individuals in 

 both the European and native population, but because of its association 

 with certain industrial diseases. 



Much the most important industrial disease in South Africa is the 

 silicosis produced in the extraction of gold from the conglomerate, both the 

 pebbles and the matrix consisting of quartz. The gravity of pneumo- 

 coniosis depends largely on superadded tuberculous infection to which the 



