W. Nicoll 
165 
It has been maintained by several observers that in some cases 
unfertilised eggs occur and that these will not develop. The occurrence 
of unfertilised eggs, however, is categorically denied by Looss. Such 
an explanation cannot, therefore, account for the non-development of 
the eggs in certain cases. While admitting the possibility that unfer¬ 
tilised eggs might occur very occasionally, Looss asserts that he has 
never once observed them nor, to his belief, has anyone else. Personally 
I have never met with any indications which would lead me to suspect 
the presence in fresh faeces of unfertilised eggs. Much more important 
appears to be the condition of the faecal material. It may vary in 
consistency from dry, hard and firm masses to the opposite extreme 
of an almost watery fluid. Normal, well-formed human faeces usually 
contain about 70-75 % of water. Where eggs are present in such 
faeces they can usually be readily cultivated. When less moisture is 
present in the faeces and consequently they are firmer and harder, 
cultures can still readily be made by the addition of sufficient water. 
It is generally in the case of soft diffluent faeces that difficulty is 
experienced in obtaining satisfactory cultures of larvae. These stools 
are usually of a light clayish consistency and are evil smelling. 
Frequently even in what appears to be a normal stool one is encountered 
which is conspicuous by its unnatural odour. In such cases there is 
difficulty in getting satisfactory cultures. 
If such vile smelling or watery stools are allowed to remain as they 
are, they will in most cases, even though heavily charged with eggs, 
give a very poor culture of larvae or even none at all. This is an 
experience which has been encountered by most observers who have 
taken the trouble to investigate the matter, and it has been my 
experience, not only with human infection, but also with infection in 
dogs and cats. If, however, such faeces be carefully and repeatedly 
washed, and the eggs sedimented, it is frequently possible to obtain 
a rich culture of larvae from even the most unpromising of material. 
Looss has also foimd that when such faeces are thoroughly mixed with 
bone charcoal satisfactory cultures may not infrequently be obtained. 
It may, with some confidence, be expected that such stools under 
natural circumstances will produce few, if any, larvae unless they are 
affected by outside influences such as rain. 
It is not easy to advance any hypothesis with regard to the matter. 
It appears reasonable to assume that in such stools some substances 
are present, deleterious to the hook-worm eggs or larvae. Whether 
these be normal physiological substances, produced under natural 
