512 PHYSIOLOGY CHAP. 



from our subject. It is only necessary to remark that there is 

 this difference between the views of Munk and Loeb. Accord- 

 ing to Munk, the brainless animal has lost all its senses, including 

 sight and hearing, as assumed by Floureus. Loeb, on the contrary, 

 does not deny, but even confirms, the observations of Schrader on 

 pigeons and of Goltz on the brainless dog, but he holds that these 

 animals, while more or less guided reflexly by sensory impressions, 

 have no trace of consciousness, because they are destitute of 

 associative memory. 



So long as there is no evidence to the contrary it may be 

 maintained that brainless animals are in a state of severe dementia 

 because they have lost memory and perception, but are capable, 

 of elementary internal and external sensations, by which their 

 automatic and reflex movements are regulated. 



At a later point we shall discuss this question, and endeavour 

 to differentiate between the concepts of perception and of sensation. 



VII. To determine the functional importance of the mesen- 

 .cephalon and thalameucephalon we need only sum up briefly the 

 results of the other experiments by which it has been attempted 

 to excite or destroy these parts separately, in order to examine 

 the effects and deduce conclusions as to their functions. 



Direct stimulation of the roof of the mid-brain, which is 

 represented in birds, amphibians, reptiles, and fishes by the optic 

 lobes or corpora bigemina, in mammals by the corpora quadri- 

 gemina, gives positive results to electrical, mechanical, chemical, 

 and thermal excitation. 



In the frog, electrical excitation of the optic lobes produces a 

 movement of the head towards the opposite side and upwards, 

 and sometimes also provokes quacking. According to Wilson, the 

 beats of the heart are slowed also. Chemical stimulation, as by 

 a crystal of sodium chloride applied to the optic lobes of the 

 frog, prolong the latent period of the movements evoked by the 

 cutaneous excitations ; sometimes there is complete inhibition of 

 reflexes, particularly if the cutaneous stimulus is of a painful 

 rather than a tactile character (Setschenow). 



The optic lobes of amphibia contain centres which control the 

 sexual clasp. Albertoni demonstrated on toads and Tarchanoff 

 on tadpoles that mechanical stimulation, as pricking with a pin, 

 squeezing with a forceps, of the optic lobes at once ends the clasp, 

 while the same stimuli applied to the hemispheres and optic 

 thalariii have no effect 011 it. They interpret these observations 

 as meaning that there are inhibitory centres of the clasp in the 

 optic lobes, which are thrown into activity by the mechanical 

 stimuli. According, on the contrary, to Baglioni (1911) from 

 his recent experiments on toads, these are not inhibitory centres 

 but true excitatory centres of the clasp, which are in tonic activity 

 during the embrace, and are profoundly injured and put out of 



