602 ANNUAL REPORT 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. 
