Overall, this is a groundbreaking book that offers important insights into bilingualism and language contact. Although the dissertation was written in the 1950s, it is still highly relevant. It raises important questions in the field of bilingualism and language contact, such as questions regarding the direction and nature of cross-linguistic influence and the borrowability of linguistic elements. These questions are still a topic of debate. In addition, the book addresses methodological issues and is an inspiring example of well-conducted fieldwork. Finally, it shows the importance of comparative research to better understand the outcome of bilingualism at different levels.

- Antje Muntendam, Radboud University Nijmegen, in Journal of Sociolinguistics 17-2 (2013) pag. 257-260.,

The importance of this volume lays first in the fact that, until now, few linguists have been aware that the main themes of LiC were first proposed in embryonic form here and even fewer had access to it. Besides its undeniable utility, the book is pleasant reading also thank to the inclusion of photos, hand-drawn diagrams and other material personally prepared by the author.

- Ilaria Fiorentini, University of Pavia/Free University of Bozen, on Linguist List 22. 4961, 2012,