34 PSYCHOLOGICAL EFFECTS OF ALCOHOL. 



AVAILABLE HUMAN REFLEXES. 



A considerable number of relatively simple neural arcs are available, 

 even in human subjects, for more or less accurate quantitative study. 

 Some of them have assumed considerable diagnostic importance with- 

 out a corresponding development of satisfactory quantitative tech- 

 niques. The swallowing reflex, the skin reflexes, the semicircular- 

 canal reflexes, the pupil reflex, the corneal reflex, and many of the 

 tendon reflexes are in regular clinical use. But their clinical investi- 

 gation is generally satisfied by cataloguing the case under one of three 

 or four general categories, such as absent, depressed, moderate, and 

 exaggerated. Change of a case from one category to another repre- 

 sents a relatively profound disturbance. Accurate techniques for 

 measuring small differences would perhaps be too time-consuming for 

 clinical purposes. Their development for special experimental investi- 

 gations has followed the development of definite experimental problems. 



While none of the available reflexes may be ignored in a study like 

 the present, certain of them have a better experimental status than 

 others. Such, for example, are a few of the tendon reflexes, particu- 

 larly the patellar reflex and the Achilles reflex, the pupil reflex, and the 

 protective lid-reflex. Experimental techniques for the measurement 

 of these reflexes have been developed so that they are dependable. 

 This was our main reason in selecting the patellar reflex and the 

 protective lid-reflex for immediate investigation. In choosing these 

 two arcs we were also influenced by several other considerations. It 

 seemed advisable: (1) to study the effect of alcohol on the nervous 

 system at as widely different reflex levels as practicable; (2) to use 

 reflex arcs of similar latency, and presumably similar complexity; and 

 (3) to avoid fatigue and adaptation phenomena. 



The patellar reflex appeared most suitable as a representative of the 

 lowest spinal level. On a variety of grounds one would have preferred 

 the Achilles reflex. For instance, it is less subject to accidental ana- 

 tomical conditions than the patellar reflex. That is, length of tendon 

 and the underlying cushions of connective tissue effect less extreme indi- 

 vidual differences in the Achilles than in the patellar reflex. Opposed 

 to this advantage are certain technical difficulties in recording the 

 Achilles reflex from the thickening of isometric muscle, and the practical 

 necessity for the subject to assume an unusual position with more or 

 less variable antecedent muscular activity. The patellar reflex, on the 

 other hand, can be recorded from a sitting or reclining subject without 

 moving him from the position he would naturally adopt for other 

 neuro-muscular measurements. Moreover, if the leg is prevented from 

 moving, quadriceps thickening may be registered from practically iso- 

 metric muscle by direct recording levers, resting on the anterior thigh. 



Reflexes of the higher levels are perhaps best represented by those of 

 the eye. In particular, the pupil reflex deserves and has received 



