THE CHEMISTRY OF SLEEP. 233 



enciug and promoting its production without danger or detriment 

 to general health. The few facts we have so far may be stated 

 as follows : In healthful sleep the blood circulates more slowly ; 

 hence kidney action and perspiration diminish. The breathing is 

 slower, and the exhalations of moisture and carbon dioxide from 

 the lungs are less. Hence, these are doubtless produced in smaller 

 amount, as they should be, from the diminution of muscular work 

 and of combustion of animal fiber. And it is highly probable, 

 though not yet fully tested by experiment, that certain gaseous, 

 vaporous, or other products of the transformation of the muscles, 

 nerves, and other tissues, partially stored up in the blood during 

 working hours, are eliminated during sleep by the lungs, skin, 

 and kidneys. The digestion is stated to be more active during 

 normal sleep, and the temperature in the vital organs at least is 

 stated by some authorities to remain at its normal point, though 

 in the limbs it probably falls. This may be due to a tendency of 

 the blood to the internal digestive organs. It is known, as was 

 proved independently by Hammond and Durham, that the volume 

 of the brain diminishes during natural sleep. 



Returning to the old edition of the Encyclopaedia Britannica 

 (1779) before quoted, a few sentences possessing interest may be 

 further taken from the article on Sleep. Referring back to the 

 article on Dreams, it is here added: "Sleep we have shown to 

 arise immediately from the communication between our sentient 

 principle and external objects being cut off, in consequence of 

 which memory is also lost, and the person becomes insensible of 

 existence. This state may be induced either by such causes as 

 affect the brain, the nervous system, or the blood, though it prob- 

 ably depends in most cases on the state of the vital iiuid." This 

 " vital fluid " or " vital spirit," as it is elsewhere denominated, is 

 apparently not the blood itself, but an agent or influence then 

 unknown, believed to reside therein. If we were now with our 

 present chemical knowledge to substitute for " vital fluid " oxy- 

 gen of oxyheemoglobin of the arterial blood, this part of the cita- 

 tion would become rational. Oxygen, however, had then been 

 discovered but four years previously, and its functions must have 

 been yet but vaguely understood. The Italics have been intro- 

 duced into the above excerpt to emphasize certain notions about 

 sleep whose fallacy has been previously pointed out. 



Dr. Hammond suggests that in the most profound natural 

 slumber the spinal cord, with its nervous ganglia, remains awake, 

 though not quite so much so possibly as when the brain itself is 

 wholly conscious. Of course, the involuntary muscles, as those 

 w-hich operate the heart, the respiratory organs, etc., governed by 

 ganglia of the spinal cord, never slumber. Their slumber is the 

 last sleep of all. But Dr. Hammond cites proof independent of 



