Perhaps they didn't want to know the soldiers about the effects of chemical warfare as this could have lead to a decline of morale and willingness to fight.
Another simple explanation is that no one understood the effects of chemical injury on the brain well and no one could give a clear answer. Then as always, the shrinks took over and claimed they fully understood the illness and were able to treat it. If it didn't work they blamed the victim not the therapy.
I fear that I am taking this thread back some way, as it has moved on whilst I have been otherwise engaged. However it might be of interest to some to tie up this loose end.
"Both gas experts, Colonel Elliot and Colonel Soltau, referred to the fact that gas is a very potent cause of functional disturbances of the nervous system, and especially were they to arise as a result of the arsine group of arsenic compounds.
Arsine in a concentration of one in ten to fifteen million has a profound mental and moral effect in addition to its slight physical effects. The physical effects are rapid and very transient, and arsenic as the Germans used it, caused few fatalities. From the point of view of knocking out men temporarily, and setting up a chain of nervous symptoms, it was the best gas they could possibly have used.
It reduces the vitality in one in forty million concentration, so that many emotional cases may arise as a result of the infinitesimal dose."
This quotation is taken from The Report of the War Office Committee of Enquiry into Shell Shock" of 1922, page 108. It is curious that this was known but has never received much publicity. It seems to have been forgotten by all except Chipmunk1.
Why this is relevant to the current thread is that the authorities seem to have been quite happy for diagnoses of "emotional" shell shock, or neurasthenia, to be made despite their own experts being fully aware of possible aetiology consistent with reported and observed physical symptoms.
The experts views on the concentrations might indicate Allied research on the subject. These opinions seem very odd when compared to the general lack of information as to usage of these gases, in comparison with the better known ones. There may have been a mutual interest in not proclaiming this information too loudly.
Fortunately this Report was not a complete waste of time and valuable lessons could be learned by future researchers:
"Unfortunately we have been unable to obtain any reliable statistics covering cases of shell shock. It would have been desirable to record the number of cases of the disorder under the general term "shell shock," and to supply tables giving figures of the varieties of disorder classified under that head. The Committee have failed to obtain this information. Much statistical matter was unavoidably lost during the progress of the war, and other material of a statistical kind, buried in the archives of the War Office and other Departments, is at present inaccessible. The Committee were advised ...that it could not, in fact, be obtained without a prohibitive amount of labour and expense......" Page 7
I think they forgot to add that much had been force fed to regimental mascots.