120 



WALTER NEUHAUS 



experiments with ethyl mercaptan, the others with skatole. Formaldehyde 

 and a mixture of many aromatic substances were also tested. All sub- 

 stances gave positive responses. 



All the results were not as obvious as those shown in the figures. Some- 

 times there were spontaneous variations in the respiration without any 

 known causes, which could appear when a water control was tested. Some- 

 times it was impossible to avoid extraneous disturbances. Finally some of 

 the responses were not quite clear. Thus the results had to be classified in 

 three groups: (1) positive reaction to smell or to water, (2) absence of 

 reaction, (3) doubtful. 



Fig, 14. Record of the respiration of goose No. 3. Skatole. 



S* 



Wi 



Fig. 15, Record of the respiration of goose No. 3. Skatole and water. 



A^yv^v, 



Fig, 16. Record of the respiration of goose No. 3. Si<:atoIe. 



Under careful consideration of all critical points of view, Table 2 was 

 set up. Skatole is the only odorous substance which has a "pure odour " 

 in the sense of v. SkramHk (1924), while formaldehyde, ethyl mercaptan and 

 also the aromatic mixture are " common odours ", which stimulate 

 not only the olfactory receptors but also the free nerve endings of the 

 trigeminal nerve in the nose. This is particularly true for formaldehyde. 

 This classification is proposed for man, and may not be valid for birds. 

 Thus it was thought that only the "pure odour" of skatole should be used 

 for further discussion. Accordingly the experiments contained in Table 3 

 were performed. The difference between the water and skatole figures is 

 large, but may be not immediately convincing. The X'^ test was used to 

 investigate the probability for the frequencies in the three classes for water 



