SELF-REGULATION 11 



conditions which are always artificial and often unnatural. This 

 statement applies more especially to the so-called method of extirpation 

 which so frequently represents the only experimental resource at the 

 disposal of the physiological anatomist. This method consists in the 

 removal of a given organ or structure hy means of an operation, the 

 subsequent continuance of a particular function being regarded as 

 proof of its connection with the. excised structure, while cessation of 

 the same function is interpreted in the opposite sense. This procedure 

 may, however, easily lead to false conclusions for two distinct reasons. 

 In the first place, a serious operation often gives rise to " shock," that 

 is to say, to a condition of temporary or permanent general depres- 

 sion or paralysis ; this effect may in reality be responsible for the 

 lapse of a function, with which the extirpated organ is erroneously 

 credited. It would clearly be dangerous to conclude, on the basis of 

 an extirpation experiment, that a particular physiological process had 

 ceased because the active organ had been removed, when it might be 

 shock that was actually responsible for the observed cessation of 

 activity. It is especially in connection with work upon irritability 

 that errors of this kind are constantly Hal tie to vitiate the results of 

 experiment. Only careful study of the shock-phenomena themselves 

 can enable the physiological anatomist to cope with this difficulty to 

 some extent. 



An equally serious cause of error in connection with extirpation 

 experiments is the faculty of self-regulation, of which every organism is 

 in some degree possessed. A mutilated organism generally " makes 

 shift " to the best of its ability and is often able to transfer the 

 duties of an excised organ to a different structure, and in this way 

 to carry on the threatened function, not indeed with unimpaired 

 vigour, but still to such an extent that the organism as a whole 

 manages to survive. Neglect of this factor is responsible for the 

 erroneous assumption that a structure necessarily cannot be the instru- 

 ment of a particular function, if the latter persists in some degree 

 after the structure in question has been excised. To take a concrete 

 instance : Both anatomical and experimental data led the author to 

 regard the so-called aleurone-layer of grasses as a glandular tissue 

 which supplies the bulk of the diastase that is required for hydrolysis 

 of the starch contained in the mealy portion of the endosperm. Other 

 investigators have subsequently shown that an isolated grass-endosperm 

 can, under certain conditions, hydrolyse its store of starch even after 

 the aleurone-layer has been removed by an operation. But this result, 

 obtained by the method of extirpation, by no means proves that the 

 aleurone-layer plays no part in connection with the hydrolysis of 

 starch under normal conditions ; all it does is to demonstrate that the 



