METHODS. 175 



We shall describe a few of the more important experiments, and summarize 

 the results of the others that bear on the main problems here under discussion. 



The principal method of obtaining the normal reflexes \y^s to place healthy 

 crabs on their backs on some convenient table, allowing the posterior end of the 

 abdomen to hang over the edge. After a few minutes their muscles relax, and 

 unless disturbed, they remain perfectly quiet for a long time. Meantime, local 

 stimuli may be applied which, if a little care is exercised, usually produce very 

 definite reflexes without arousing the animal from its comatose condition. 



The usual stimuli for the chewing reflexes, were drops of clam juice, or pieces 

 of clam, or the like, of the same temperature as the air; and a breath of warm air, 

 or the gentle touch of the finger tips, for the crossed thoracic, the abdomino-thor- 

 acic, or other temperature reflexes. Various other stimuli were also used from 

 time to time, as indicated in the description of results. Having familiarized 

 myself with the normal reflexes, the brain or cord was sectioned in various ways. 

 After the recovery from the shock, which lasts from five minutes to an hour or 

 two, the crab was tested as before and the difference in behavior noted. 



The operations were performed in various ways, the principal difficulty being 

 to avoid the great loss of blood following any puncture of the skin near the brain 

 or cord. 



When the section had to be accurately located, there was no way but to thor- 

 oughly bleed the animal, expose the parts, and section as desired at leisure. This 

 was the method followed in transecting one-half of the abdominal cord at a given 

 point, and in cutting it in halves lengthwise. 



In transecting the collar, the animal was tied down and the legs fixed in a 

 convenient position; a quick cut was then made across the collar, care being used 

 to keep the opening in the skin as small as possible. To prevent the loss of blood, 

 that spurts with great force from the opening, the wound was instantly 

 plugged with a tight fitting wad of absorbent cotton smeared with vaseline. If 

 the operation is successful, very little blood is lost, the animal quickly recovers, 

 and may live for six or eight weeks, or longer. 



The principal errors to be guarded against arise from the difficulty of 

 making the sections in the desired place, and from the degeneration of the wounded 

 or isolated parts of the brain. In some cases, an isolated segment of the nerve 

 collar would degenerate and completely disappear in a few days after the operation; 

 or the degeneration may extend into other parts of the brain and vitiate the results. 

 In some of the most successful cases, the cut surfaces of the brain, after a lapse 

 of several weeks, were covered with an incrustation which, if removed, left the 

 surfaces almost as clean and sharply defined as when the wounds were 

 first made. 



To check these sources of error, we have made careful post-mortem examina- 

 tions and have excluded all those experiments in which there is any doubt about 

 the location of the wound, or the extent of the degeneration. 



