300 T. Brailsford Robertson: 



for such a conclusion would seriously conflict with much thera- 

 peutic and pharmacological evidence; moreover Landois^) and 

 Maxwell') have shown that Creatin stimulates the motor areas 

 of the cortex and Maxwell has demonstrated that this effect 

 is due to Stimulation of the grey matter. We are furthermore 

 in possession of the fact, to which I have alluded, that an 

 increase in the COg tension of the blood supplied to the brain 

 at first accelerates and later, if the increase in COg tension 

 be sufficiently great, inhibits the rhythmic discharge of Im- 

 pulses from the respiratory centre or centres. It thus appeared 

 possible that although the ordinary nerve-stimulants do not 

 excite nerve-cells, yet some other group of substances might 

 be found which does so. Accordingly the foUowing experiments, 

 of which I hope to give a fuller account elsewhere, were 

 undertaken. 



The roof of the skull, in frogs, was removed by means 

 of a fine pair of bone forceps as far down as the tip of the 

 fourth ventricle; in some instances the membrane covering 

 the floor of the fourth ventricle was removed, in others not, 

 but doubtless in nearly all instances it was perforated. The 

 cerebrum was removed by cutting across the thalamencephalon 

 just in front of the optio lobes; by this means it was found 

 that a more regulär respiratory rhythm was obtained, the frog 

 was quieter, and the results were more uniform. The cavity 

 left in the skull by the removal of the cerebrum was then 

 plugged with absorbent cotton and absorbent cotton was placed 

 all round the wound so as to absorb any fluid which might 

 escape from the depression left by the removal of the roof of 

 the skull. With practice the Operation could be performed in 

 from 3 to 4 minutes, and, if successful, within from 3 to 

 5 minutes after the Operation respiration, which at first is 

 Buspended, is resumed. After from 5 to 10 minutes, the rhythm 

 of respiration usually becomes constant, and, if the frog be 

 left untouched, remains so for over two hours. 



After an interval of 15 minutes, to allow all shock effects 

 to subside, drops of various Solutions were placed upon the 



^) Landoia. Deutsche med. Wochenschr. 13, 685. 



2) S. S. Maxwell, Joum. of Biolog. Chem. 3, 21, 1907. 



