Between 1930 and 1945 Carrillo contributed valuable original research on glial cells and the method for staining and observing them under the microscope, as well as on their evolutionary origin (phylogeny), and the comparative anatomy of the brain across the several classes of vertebrates. He also contributed novel techniques for neurological diagnosis: he refined iodine-contrasted ventriculography, called iodoventriculography, and discovered signs in it for several diseases; developed tomography, which by lack of electronic means at the time was prevented from integrating computation yet was a precursor of what is today known as computerized tomography; and achieved its combination with electroencephalogram (EEG), termed tomoencephalography.