be decided for each separate case. Every research, which has not been carried out with absolutely unobjectionable technique, delays our arrival at a clear appreciation of the suitability of the methods. There are practically no methods which, on first acquaintance, will lead anyone to good results. Often weeks have to be spent in preliminary studies, before facts are acquired which entitle us to apply the required methods to certain questions. No conscientious student would publish these preliminary studies, but would treat them as exercises. Owing to a very extensive experience of my own, I cannot deny that many preliminary studies of this kind have been published. It is only work that is deliberate, and that is based on a complete command of methods, that can lead to satisfactory results. It is, besides, the duty of the clinical worker to thoroughly study each case, and to follow it out to the end.
As yet, it is too early to criticize the works that have appeared, and I have contented myself merely with summarizing such as have come to my notice. Then the results of recent experimental researches have been referred to. The question of the specificity of the substrates is discussed, and, finally, in the description of the technique, some recent experiences have been considered.
November, 1913.
