602 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1911. 



If the need of sleep is due to an accumulation of toxic waste pro- 

 ducts in the organism, one ought to be able, by injecting these sub- 

 stances into a normal animal, to communicate the necessity for sleep. 

 Our first experiments in that direction were unsuccessful. By 

 injecting into a vein of a normal dog some blood or serum taken from 

 a dog exhausted by loss of sleep, we had no very definite results, 

 although in some cases we brought on some modifications of the cells 

 of the frontal lobe, and by injecting these same substances directly 

 into the brain we were no more successful. Could it, therefore, be 

 concluded that wakefulness is not accompanied by the accumulation 

 of toxic substances, and is caused only by the impoverishment of the 

 nerve cells? This conclusion was possible, but it might equally be 

 the case that the blood of the normal animal destroyed the substances 

 injected in small doses, or that their quantity was too small. To 

 remove this last doubt we made our injections by another method. 

 There exists, in the interior and around the nerve centers, a liquid 

 called the cerebro-spinal fluid, which completely envelops them. 

 You can get this fluid either at the lower end of the spine, and is there 

 reached by lumbar puncture, and in spinal anesthesia, or between the 

 occipital bone and the first vertebra, at the level of the fourth ven- 

 tricle of the brain, and it is there that we operated. To be sure, the 

 operation is a delicate one, but it can be performed with a little 

 practice. By observing certain necessary precautions, such as avoid- 

 ing compression, one can without danger or trouble make injections 

 at that level. The serum, or, better yet, the cerebro-spinal fluid, of an 

 animal exhausted by loss of sleep, if injected under these conditions 

 into a normal animal, produces in the latter in about half an hour an 

 imperative need of sleep. The animal so injected is benumbed little 

 by little, its eyelids blink, its limbs relax, its* eyes close, it loses all 

 attention, and it responds but feebly to strong stimulation. Its brain 

 presents the characteristic lesions of insomnia. The injections, under 

 the same conditions, of liquids from a normal animal have no effect 

 at all. You, therefore, may conclude from these experiments that it 

 is possible to transmit the absolute need of sleep from an exhausted 

 animal to a normal one, and also that the liquids of exhausted animals 

 have a property or contain a substance capable of producing sleep. 

 If it is indeed a substance, do you ask me what it is ? I can not yet 

 tell you. It is that very research which is at the present moment 

 occupying our attention. 



This rapid review of the question of sleep will have shown you that 

 it is a most complex problem. I would wish that it would likewise 

 give you the impression that although physiology alone can not 

 dream of solving the problem, it can at least offer a profitable contri- 

 bution, and that its share, when it is contented with facts, is not less 

 than the contributions of other sciences that are busy with the same 

 problem. 



