Philosophical Conceptions of Life. 261 
point out that the recent investigations of Francois Frank * 
would seem to indicate that the variations of temperature 
actually observed are chiefly due to changes in the eerebral cir- 
culation. Plunging suitable sounds, connected with a thermo- 
electric apparatus, into the brains of animals to different 
depths, Frank found that the deeper parts of the brain are 
always warmer than its superficial layers. The superficial 
layers are continually cooled by radiation, and their tempera- 
ture is a degree, or more than a degree, centigrade lower than 
that of the deeper parts. Even these, however, are from 1° 
to 2° centigrade cooler than the blood in the thoracic aorta ; and 
it will therefore readily be understood that a relaxation in the 
‘muscular coats of the cerebral vessels, permitting the more 
rapid circulation of a larger quantity of blood, would be 
promptly followed by an increase in the temperature of the 
superficial parts of the brain. None of the observers I have 
cited have reported a surface temperature of the head during 
mental effort that is too high to be accounted for in this way ; 
and if, as I willingly concede is probable, there is really an in- 
creased heat-production in the brain itself, it is wholly masked 
by the more considerable change due to afflux of blood. | 
Now a consideration of the phenomena of blushing, and 
certain well-known sensations in the head, might lead us to 
expect that emotional and mental conditions would prove to 
be attended by increased activity in the circulation of the 
blood in the brain; yet many difficulties have hitherto been 
encountered in the attempt to demonstrate experimentally that 
this is true. Mosso of Turin supposed that he had succeeded 
in doing this with his plethysmographt. The instrument is 
essentially a cylinder of water, into which the arm is intro- 
duced and so fastened in place by a caoutchoue membrane 
that the slightest increase or diminution in the volume of the 
arm will cause the rise or fall of the water, through a tube 
connected at one end with the interior of the cylinder and at 
the other with a suitable recording apparatus. The pen or 
pencil of this apparatus inscribes a curve that rises or falls 
with the fluid in the tube. Among the curious observations 
made with this instrument, Mosso reports that the mental 
operations and emotions of the persons he experimented on 
* Francois Frank, Communication to the Société de Biologie, May 29, 
1880, in Gaz. Hebd., June 11, 1880, p. 392. 
t+ Angelo Mosso, ‘ Sopra un nuoyo metodo per scrivere i movimenti 
dei vasi sanguini nell’ uomo,” Atti della Reale Accademia delle Scienze 
di Torino, t. xi., Nov. 14, 1875. Ihave not obtained access to the ori- 
ginal, but find an abstract inthe Archives de Phys. norm, et path. 1876, 
p- 175. See also Barker, p. 12, op. cit. supra. 
